Ammo production is based on demand. Demand is based on the number of firearms chambered for a certain cartridge in use.
My guess is there are a lot of 38 Spl and .357 revolvers out there in use. So I don't expect the ammo manufacturers to abandoned that market.
Same with 9mm and 45 ACP. Too many pistols out there and owners that want ammo. With 40 I have no idea.
A search of .223/5.56 rifles on GB will lead one to believe that there are a lot of rifles out there. Ammo will be available for those. 308/7.62 maybe.
I don't have any insight to anything else. I wouldn't bet that some of these newer cartridges (this century) won't be a roll-your-own proposition in a few years.
The market has been very unpredictable for several years now. That's not a good sign.